Frequency control system



April 10, 1934. R. M. PAGE 1,953,973

FREQUENCY CONTROL SYSTEM File /Ma 28, 1930 2 Sheets-Sheet 1 INVENTOR. MAW/l 91%- 594x 44 BY W M ATTORNEY April 10, 1934. R M PAGE 1,953,973

FREQUENCY CONTROL SYSTEM Filed May 28, 1930 2 Sheets-Sheet 2 T.& F

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2mm 9% 8034/, BY WW A TTORNEY Patented Apr. 10, 1934 UNITED STATES PATENT OFFICE 3 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) My invention relates broadly to frequency control systems and more particularly to a circuit arrangement for maintaining the transmitting frequency in a signaling system.

| Gne of the objects of my invention is to provide a circuit arrangement for a frequency control system in which the frequency of a self-oscillating circuit may be maintained in synchrcnism with oscillations generated by a standard oscillator. 7

Another object of my invention is to provide a circuit arrangement for a frequency control system in a signal transmission apparatus in which an intermediate circuit is arranged between a standard oscillating circuit and the oscillator system of a signal transmitter, the intermediate circuit being adjusted to maintain the standard oscillating circuit and the oscillator system of the transmitter in synchronism, whereby the transmitting frequency may be maintained constant.

Other and further objects of my invention reside in the circuit arrangement for controlling the frequency of a transmission system as set forth more fully in the specification hereinafter fol lowing by reference to the accompanying drawings, in which:

Figure l diagrammatically illustrates a frequency control system embodying the principles of my invention in which the tuning device which controls the frequency of the oscillating circuit is electrostatically actuated; Fig. 2 illustrates an arrangement of automatic tun ng device in the circuit intermediate the standard oscillator and the oscillating circuit of the transmitter in which the tuning device is magnetically controlled; Fig. 3 is a perspective view illustrating one form of variable capacity device which may be employed for controlling the frequency of the oscillating circuit of the transmitter; Fig. 4 is a perspective view of the electrostatic drive and variable condenser system which controls the frequency of the transmitter; Fig. 5 illustrates a curve indicating the time relation between the standard and the transmitter waves for various phase angles between these waves from O to 360 degrees; Fig. 6 is a curve showing how these waves add in the mixer tube for the various phase angles. As the phase shifts from 0 to 360, the amplitude of the input to the mixer tube, denoted by 0, goes from 50 maximum at 0 to minimum at 180, and back to maximum at 360; and Fig. 7 is a curve showing the rectified output of the mixer tube which may appear as a voltage across a high resistance, or as a current through the output circuit of the mixer tube.

My invention is directed to a frequency control system for signal transmitters in which electron tubes of low power are employed in the circuit of a standard oscillator and in an intermediate circuit disposed between the standard oscillator and the oscillating system of a signal transmitter. By the circuit arrangement of my invention, I secure a marked advantage in the operation of a transmitter by reason of the fact that low power receiving tubes may be employed in the frequency control circuits which connect to the oscillating system of the signal transmitter as distinguished from transmitter tubes of relatively larger power heretofore required in the circuits in which frequency control is effective. I provide a standard oscillator of low power which may be controlled by the constant frequency characteristics of a piezo electric crystal. The output of the low power piezo electric crystal controlled oscillator is supplied to a mixer circuit. The mixer circuit 76 includes a rectifier tube of low power, in the output circuit of which there is arranged an angularly movable element which is capable of change in angular position in accordance with changes in frequency of the transmitter signaling energy. 80 The angularly movable device may be an electrostatically operated member or an electromechanically operated element, either of which may be adapted to control a variable impedance element arranged in circuit with the oscillating system of a signal transmitter. A portion of the high frequency energy in the radiating circuit is coupled back upon the mixer circuit and tends to beat with the oscillations developed bythe standard oscillator. The oscillations in the standard oscillator and from the radiating circuit combine in the mixer circuit. The beat current is rectified and operates the angularly movable device which controls the variable impedance element in the oscillating system of the signal transmitter. Changes in current in the mixer circuit due to the differential action of the currents supplied thereto from the standard oscillator and from the radiating circuit shift the angular position of the variable impedance element in the oscillating circuit of the signal transmitter and automatically control the frequency of the oscillating circuit, thus tending to bring the oscillating circuit back to a predetermined frequency under conditions of variation of the signaling frequency. The tuning vernier in the oscillating circuit may be either electrostatically or electromagnetically controlled and may vary either the capacity or the inductance of the tuned circuit of the oscillator. The standard oscillator and the oscillating system of the signal transmitter are thus maintained in synchronism. A small crystal oscillator and amplifier employing receiving tubes may thus be used to control the oscillator system of the transmitter in lieu of the high power transmitter tubes heretofore employed in a crystal control oscillator and amplifier circuit for signal transmitters.

The high power oscillator of a signal transmitter may be controlled on a predetermined harmonic of the crystal frequency or on a harmonic of a sub-multiple of a reference frequency obtained through frequency division. The system of my invention makes it possible to maintain the frequency of a self-oscillating circuit in any of several fractional or multiple relationships with respect to a standard or reference frequency although the amount of energy available from the standard or reference frequency may be very small.

Referring to the drawings in more detail reference character 1 designates the antenna system of a radiating circuit including the ground connection 2. A high frequency oscillator constituted by electron tube 3 has its output circuit coupled with the antenna ground system 1-2. The input circuit of the oscillator 3 is tuned by means of resonant circuit 4 across which there is connected the variable tuning element comprising condenser 5. The variable tuning element consists of a rotor 6 and a stator 7 connected across the input circuit of the electron tube 3, the arrangement of which is shown more clearly in Fig. 3. The rotor plates 6 are carried by angularly movable shaft 8 which is mounted in bearings 9 and 10. The shaft 8 is biased in a predetermined position by means of spiral spring 11 and is adapted to be shifted in a counterclockwise direction against the action of spring 11 from a normal predetermined position, or in a clockwise direction which tends to wind the spring 11 and store energy therein tending to restore the condenser to normal position when the frequency conditions of the oscillator have been restored to normal, thus varying the effective capacity between rotor plates 6 and stator plates 7 across the input circuit of the high frequency oscillator 3. The shift in the angular position of the plates 6 and 7 is effected electrostatically as illustrated in Fig. 1 by the electrostatic actuator constituted by rotor plates 12 mounted on shaft 8 and stator plates 14 with respect to which the rotor plates 12 are angularly movable. The plates 12 and 14 are disposed in parallel with the outputcircuit of the oscillator and are shunted by the impedance 15 across which a potential drop is produced for varying the magnitude of the charges imparted to plates 12 and 14, thereby varying the electrostatic attraction thereof and tending to angularly shift the shaft 8. The rotor plates 12 are so shaped with respect to the stator plates 14 that changes in the electrostatic charges impressed upon the rotor and stator plates tend to attract or repel the sets of plates one with respect to another, thus imparting angular motion to shaft 8 for correspondingly changing the overlapping relationship of plates 6 and '7. The plates 12 are normally positioned with respect to plates 14 under control of the bias of spring 11 so that variations in the electrostatic charges impressed upon plates 12 and 14 tend to change the spacial relation of the sets of plates 12 and 14. The impedance 15 is connected in the output circuit of the intermediate or mixer circuit which includes electron tube 16. The output circuit of electron tube 16 also includes high potential source 17 and by-pass condenser 18. The input circuit of electron tube 16 includes the secondary Winding 19 of coupling transformer 20 and the grid leak and grid condenser 21. Tuning condenser 22 is connected across the secondary winding 19. The mixer or intermediate circuit is connected with the output of a standard crystal control oscillator having the primary winding 23 of the transformer 20 in the output circuit thereof.

The standard oscillator is shown more clearly in Fig. 2 as including electron tube 24 having its input circuit closed through piezo electric crystal element 25 with the grid of electron tube 24 biased by means of battery 26 through resistor 2'7. In Fig. 1, the output circuit of electron tube 24 includes B battery 28 in series with the primary winding 23 of transformer 20. A portion of the high frequency energy from the radiating circuit l-2 is coupled back from the transformer 30 in the radiating circuit by means of winding 31 through leads 32 to winding 33 which couples with the input circuit of the mixer or intermediate system including electron tube 16. In this manner high frequency energy from the radiating circuit may be supplied to the intermediate circuit, which energy establishes a beat frequency with the energy delivered by the standard oscillator which connects with piezo electric crystal 25. The beat frequency energy is rectified in the intermediate or mixer circuit including electron tube 16 and operates the electrostatic angularly movable system by variable charges impressed upon plates l2-14. To facilitate movement of the electrostatic device, these members may be enclosed in an evacuated vessel. The angular movement imparted to shaft 8 effects a change in the mutual capacity of plates 67 thereby restoring the frequency of the oscillator system including tube 3 to normal. This results in a change in frequency of the energy supplied through winding 31, leads 32, winding 33 and winding 19 to the input circuit of the mixer system thereby selectively adjusting the tuning of the oscillator system.

In lieu of the electrostatic angularly movable system shown in Fig. 1, I may employ an electromagnetic control system as shown in Fig. 2. The electromagnetic windings 34 and 35 wound on magnetic ring 36 are disposed in series with angularly movable winding 37. The angularly movable winding 37 is carried by the angularly movable shaft 8 and changes its position according to changes in the magnetic flux across the gap 39. The spring 11 tends to bias the shaft 8 in a predetermined position and angularly movable inding 37 tends to shift shaft 8 relative to the action of spring 11 thereby bringing about a change in effective capacity by the rotor and stator plates 6 and '7, respectively. This variable capacity as shown in Fig. 2 is arranged across the output circuit of electron tube 3 in series with the condenser 40. The energy derived from the radiating circuit through winding 31 and transmitted by conductors 32 to the intermediate circuit through coupled windings 33 and 19 beats with the energy generated by the standard oscillator 24 thereby changing the magnetic flux which threads angularly movable winding 37 and bringing about the required change in tuning of the oscillator circuit for restoring the oscillator to normal operating condition.

The oscillating circuit of the transmitter is maintained in synchronism with the operation of the piezo electric crystal controlled oscillator through the cooperative action of the intermediate circuit with respect to the oscillating circuit of the transmitter. The transmitter may be set for operation upon any particular frequency by proper adjustments of the oscillator circuit of the transmitter, proper design of the variable impedance in the oscillating circuit, and by selection of the crystal and constants of the standard oscillating circuit.

Fig. 4 shows more clearly the connection of the electrostatic drive constituted by rotor plates 12 and stator plates 14 with the variable condenser constituted by plates 6 and '1 connected in the transmitter control circuit.

In the operation of the automatic control system, the output E. M. F. of the curve shown in Fig. 7 tends to produce rotation of shaft 8, while spring 11 tends to oppose this rotation. It is seen from curve in Fig. '7 that as the phase angle shifts from 0 to 180, the E. M. F. tending to produce rotation of shaft 8 falls from maximum to minimum. The device must be so adjusted that at some point between 0 and 180, such as the point e, the force due to the spring will just balance the E. M. F., so that as long as the phase angle remains fixed at that point, no rotation of shaft 8 will occur.

If now the transmitter frequency increases slightly with respect to the standard frequency, the following events occur: (1) The phase angle will shift toward 180; (2) the E. M. F. output of the mixer tube will decrease; and (3) shaft 8 will be caused to rotate through a small angle. This rotation of shaft 8 is made to bring about a very slight increase in capacity (or inductance) in the tuned circuit of the transmitter, thus effecting a slight reduction in transmitter frequency to offset the tendency for that frequency to increase. Should the transmitter frequency tend to decrease, the output of the mixer tube would increase and cause rotation of shaft 8 in the opposite direction a decrease in capacity (or inductance) of the transmitter circuit resulting.

The action of the system is therefore seen to oppose any tendency of the transmitter frequency to change in either direction, irrespective of the cause of the tendency to change, so long as the standard frequency is constant.

While I have described my invention in certain preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In a frequency control system, a power oscillator, a standard frequency oscillator, a tuning element for controlling the frequency of said power oscillator, a common circuit coupled directly to said power oscillator and said standard frequency oscillator for combining the fundamental frequencies of said oscillators, and an electrostatic driving device connected in the output of said common circuit and actuated by said combined fundamental frequencies for imparting angular movement to said tuning element under conditions of change of said fundamental frequencies for maintaining the frequency of said power oscillator constant.

2. In a frequency control system, a power oscillator, a standard frequency oscillator, a tuning element for controlling the frequency of said power oscillator, a common circuit coupled directly to said power oscillator and said standard frequency oscillator for combining the fundamental frequencies of said oscillators, a single detector tube having its input circuit connected to said common circuit, an electrostatic driving device connected to the output circuit of said detector tube, a shaft driven by said device, a moving element carried by said shaft and arranged to control said tuning element, whereby the frequency and phase relationships of said oscillators may be maintained fixed by the interaction of said fundamental frequencies.

3. In a frequency control system, a power oscillator, a standard frequency oscillator, a tuning element for controlling the frequency of said power oscillator, spring means for normally causing the tuning element to occupy a predetermined position, a common circuit coupled to said power oscillator and said standard frequency oscillator for combining the fundamental output frequencies generated by said oscillators, means for deriving from said common circuit a direct current potential that is a function of the phase difference between the output frequencies of the power oscillator and the standard frequency oscillator, and an electrostatic driving device connected to move said tuning element against said spring means by an amount proportional to the potential derived by said potential deriving means.

ROBERT M. PAGE. 

